Chert (Nodule)

Physical Properties

Hardness: 6.5–7 on Mohs scale. Color: Dark grey to charcoal. Luster: Dull to waxy. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.

Formation & Geological History

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater within limestone or chalk beds. Often Cretaceous to Paleozoic in age.

Uses & Applications

Historically used for stone tools/arrowheads. Currently used in road construction, and higher quality varieties as gemstones (jasper/agate). This specific specimen is of collecting interest.

Geological Facts

Chert behaves like glass when struck, producing very sharp edges. It is often found as nodules or 'concretions' that weather out of softer surrounding rock like limestone.

Field Identification & Locations

Identify by its 'flint-like' waxy texture and shell-like (conchoidal) fractures. Look for it in riverbeds or limestone outcrops. It is sparks when struck against steel.

Identified on: 4/20/2026

Mode: Standard